Field of the Invention and Related Art Statement
This invention relates to a welding monitoring apparatus provided with a light attenuating means for dimming a part of an observed image in at least a part of an image guide.
Generally, the arc welding is extensively used in welding. However, such intensive arc light is emitted in the arc welding that it is necessary to protect the eyes of the worker. Therefore, for example, in the publication of Japanese Patent Publication No. 11755/1982, there is disclosed a prior art example wherein a non-uniform transmissivity type flter with which the transmissivity of the light in the central part becomes smaller is provided in front of an imaging tube of a monitoring television camera.
In the above mentioned prior art example, an incident light from an arc light part of a high luminance can be intercepted by the filter but, as the filter is arranged in front of the image forming plane of the image forming optical system, the light will be attenuated not only in the high luminance part but also in the peripheral low liminance part. Therefore, it is not sufficient as a welding monitoring apparatus and has a disadvantage that, while welding, the visual field will become dark and the periphery will not be seen.
In another prior art example disclosed in Japanese Patent Laid Open No. 142528/1983, a partly shielded fiter is movably provided but there is substantially the same defect as in the first prior art example.
Further, in the publication of Japanese Patent Laid Open No. 202189/1982, there is disclosed a prior art example wherein a light attenuating filter is fitted removably from the incident light by rotation.
In this prior art example, when not welding, the above mentioned disadvantage will be able to be dissolved but, while welding, the light incident from the peripheral side of a low luminance will be also attenuated, therefore, the same as in the above described prior art example, the peripheral side will become so dark as to make the observation or discretion difficult.
Also, in U.S. Pat. No. 4,225,771 and DE No. 3339182C1, there is a prior art example wherein a filter is arranged on the front surface side of a television camera to exclude the influence of the arc light in the observation.
In these prior art examples, there is a defect that, as a monochromatic picture image is obtained, the discretion is difficult.